1. Field of the Invention
The present invention relates to a control device for a vehicle AC generator which is mounted on a vehicle such as an automobile, charges an on-board battery and feeds other electric loads of the vehicle.
2. Description of the Related Art
In general, an AC generator is mounted on a vehicle such as an automobile, and by the rectified output of this AC generator, an on-board battery is charged and various electric loads of the vehicle are fed. This vehicle AC generator is driven by an engine, and since its rectified output voltage increases as the engine speed increases, the rectified output is adjusted by a voltage control device. This voltage control device monitors the rectified output of the vehicle AC generator, and turns on and off the field current of the vehicle AC generator by a power transistor so that the rectified output voltage of the vehicle AC generator falls within a specified range.
An on time ratio of the power transistor indicates a generation rate of the AC generator, this generation rate is monitored by a generation rate monitor circuit, and its monitor output is supplied to a vehicle electronic control unit (ECU). The vehicle electronic control unit (ECU) is constructed by using a microcomputer, and performs, for example, idle control of an engine by means of the generation rate monitor output.
JP-A-5-38076 discloses that an energization rate of a power transistor is detected through a collector voltage of the power transistor.
However, in the voltage control device of the vehicle AC generator, since the power transistor is turned on and off in accordance with the rectified output voltage, the on/off timing is generally random. Thus, the collector voltage of the power transistor disclosed in the above publication also rises up and falls down at random timings, and its frequency is also changed. Accordingly, in order to perform a control by the vehicle electronic control unit (ECU) using this, there is serious difficulty in designing its algorism.